Barking machines of the type mentioned by way of introduction have been known for a long time, and as an example reference is made to SE 463,660 which discloses a barking machine, in which the processing edges are formed on separate, exchangeable processing means which are supported at the outer free ends of the respective swinging arms. When a log arrives at the barking machine, the rotation of the rotator, in combination with climb-up edges formed on the swinging arms and designed especially for this purpose, results in the climbing up thereof on the front end surface of the log, such that the outer ends of the swinging arms are pivoted outwards until the edges of the processing means are applied against the circumferential surface of the log. During continued rotation of the rotator and feeding of the log, complete barking of the log is accomplished by the edges of the processing means being resiliently applied against the circumferential surface of the log and shearing off the bark helically along the circumferential surface.
To enable peeling off also of bark which is difficult to remove, such as frozen or dried bark, the force by which the processing edges are resiliently pressed against the log must be relatively great. This causes problems when practically the entire log has been fed through the barking machine and the processing edges are on the way to leave the log. With an unchanged spring load and a smaller and smaller part of the processing edges applied against the circumferential surface, the pressure in the contact surface between log and processing edge will successively increase, resulting in the processing edge cutting deeper and deeper into the log. This causes cuts in the end portion of the log and may in unfavorable cases also result in the log splitting or large pieces being cut away. Such cuts and splits must be cut away from the finished timber, implying that the earnings from the cutaway timber are lost. With optical scanning of the log, the deeper cutting in the end of the log can besides be perceived as a timber defect and result in the log being sawn in a manner which gives a lower timber yield.
The great spring load affecting the swinging arms also causes problems in other areas of a log than precisely adjacent to the rear end portion when the processing edges leave the log. In fact, most logs have knots along their length. When a processing edge hits a knot during the barking process, the swinging arm is thrown away from the circumferential surface, and it is not unusual for the processing edge to move about 5 cm or more away from the log surface. The spring load then provides for the processing edge being again pivoted to the circumferential surface at high speed and with great force. The timber is then damaged by the processing edge making pits which may have a depth of several centimeters. In unfavorable cases, such damage may cause the timber parts which are recovered from the outermost parts of the log cross-sectional area to be classified in a lower class or be rejected, resulting in a reduction of earnings. However, as a rule, the outermost segments of the cross-sectional area of a log are cut to chips for further refinement in the paper industry, but also the quality of the chips is detrimentally affected by all types of chip damage, and therefore many large pits in the circumferential surface may result in the chips being classified in a less paid class of quality. At the same time it is important that the spring load affecting the swinging arms is great such that the barking tools are pivoted back to the surface of the log as quickly as possible and as small areas as possible are left unbarked. The quality of the chips is, in fact, also affected detrimentally by an increasing amount of bark. Summing up, these demands placed on the effecting of the barking process will result in a compromise which is difficult to balance and which, in many cases, does not give a satisfactory result.